Removal of tin from lead containing tin and other impurities



April 25, 1939. T. E. HARPER. JR. ET AL 2,155,545

REMOVAL OF TIN FROM LEAD CONTAINING TIN AND OTHER IMPURITIES Filed March '25, 1958 Patented 25 1939 I UNITED STATES PATENT OFFlCE REMOVAL OF TIN FROM LEAD CONTAIN- ING TIN AND OTHER IMPURIT IES Thomas E. Harper,.Jr., and Gustave Reinberg,

La Oroya, Peru, assignors, by mesne assignmcnts, to The American Metal Company, Limiltredii New York, N. Y., a corporation of New Application March 23, 1938, Serial No. 197,672.

- In Peru July 13, 1935 6 Claims. (01. 75-78) This invention relates to separating tin from principally are occurring, namely (1) a direct impure lead which contains tin and perhaps oxidation of tin and lead, arsenic, antimony, etc. other components, and particularly to such sepaby air stirred into the bath, and (2) an oxidation ration by oxidation. of the tin by lead-oxide and other oxides, (such 5 Separation from lead of relatively small quanoxides being continuously formed by direct oxi- 5 tities of tin, arsenic, antimony, copper, etc., has dation of the air). As a result the dross which been made by the method known as softening as we obtain according to .our invention contains described in Metallurgy of Lead by H. O. Hoffthe higher percentages of tin mentioned. It also man, 1918. This process is based on the prefercontains some lead-oxide but the actual quanlo ential affinity of these metals other than copper tities of lead-oxide formed are small since the for oxygen. Thus tin oxidizesjirst, then arsenic, percentage of dross formed as compared with antimony and then lead. For such softening the the amount of metal treated is small. lead bullion is melted at low temperature to The pr c pa Object of the P t invention separate the copper as a dross. After separation accordingly is to provide a simple process for 'of the copper the temperatures are raised and separation of tin from impure lead which shall 15 the other metals are allowed to oxidize which resultin a higher concentration of tin in the rethey appear to do in the order indicated above. suiting dross, and which may be performed by 9. There always occurs in the softening furnace an s mple inexpensive apparatus excessive oxidation of lead which escapes as oxide The invention accordingly comprises the novel with the Oxides of the other metals from which it proce s a d steps of processes a well as the 20 is desired to separate it. According to Hoffman's novel apparatus and Combinations thereof book mentioned above the tin skim that rises to Carryin 0111; such D100esSeS.$Pe0ifiC embodiments the surface in the softening furnace after the Of whic e desc herein by y Of x p dross. has been removed contains about 70% leady d in accordance With the manner in which oxide and about 12.5% of tin-oxide, which means w now p e er'to pract c the n on. 25

ametallic tin content of about 9.5%. I An apparatus in which the process may be Another method has been proposed for sepacarried out s s o in the accompanying r wration of tin from lead and other alloys by air a onstituting P Of this Specification, in oxidation with stirring. The tin-oxide forms a w i dross which rises to the surface from which it is Fig 1 is a Vertical Section Shown in part 30 removed. The process is stated to produce drosses grammatically Of a kettle with a stirrer mounted containing as high as 12% tin. With low antithereon;

menial lead the content is considerably less. F g. 2 is enlarged detailed View e' Summarizing these old processes then the sofbelief o 1; and

tening process produced some concentration of is al enlarged fragmel-itary View of the 35 I tin but at the same time caused the production impeller Shown in t of a very high percentage of lead-oxidewhich In e drawing. um l indicates a hemidepleted to that extent the amount of metallic spherical steel kettle in which is contained a lead in the resulting metal recovered. The stirbath 2 of molten lead containing d w ch 40 ring process resulted in a dross whose highest may a so c ta n other impurities such as anti- 40 content of tin is stated to be 12%. mony, arsenic, etc. Mounted above the bath on W have .f und in accordan ith our i suitable supports 3 is a high speed electric motor vention that the concentration oi tin in the dross 4. This meter Operates a vertical shaft 5 ich may be increased above 12% and under preferred depends therefrom and at the ends of which is a 5 working conditions may run as high as of mounted a disintegrating impeller 6. The im- 45 tin in the dross This is accomplished by stirring Deller s t a p e ably at about half the the molten bath of impure lead containing tin depth of the bath 2. The motor 4 is capable of andother impurities such as antimony, arsenic, rotating the shaft and impeller at speeds of 900 etc. if these are present, under temperature con- R. P. M. or higher, giving a peripheral speed of ditions, and stirring speeds such that leadoxide e mpel of o e o t 2600 Per minute. 60 is produced in appreciable quantities and causes e mpe e s composed o a s eeve 'l'keye'd replacement reactions with tinto form tin-oxide t0 the s aft 5 by ey 8. From the collar and and metallic lead. Thus in accordance with our integ l ther with xt nd o r sintegrating invention under the temperature and stirring radial arms 9 'of generally elongated pyramidal as conditions mentioned two types of oxidation shape in plan view. Each outer free end of each "base of the kettle and is used for initially heating the contents and maintaining the heat of the kettle when required. When the motor 4 is operating at high speed it causes the impeller 6to form a vortex l2 in the molten metal of the bath 2. Oxidation of the tin and lead 'occurs and a dross l3 collects on the surface of the metal ,and is drawn into the vortex and from there thrown out laterally by the impeller, so that the particles of dross are disseminated through the bath as shown by the fine dots in thebath 2 in Fig. 1. This dross consists of oxides of tin and lead and other oxide impurities of metals that may be present. i

In carrying out our process primary or direct oxidation by air of the impure lead containing tin, and other components produces a substantial amount of lead-oxide and may produce oxides of the other components. The lead-oxide and tin-oxide form a dross which is continuously circulated through the bath 2 as noted. As a result of the direct oxidation of tin and the circulation of the dross containing lead-oxidethrough the bath, a. building up of the tin-oxide content of the dross occurs. We have found that using speeds of above about 900 R. P. M. with the apparatus shown in the drawing, and with maintenance of a temperature of above 950 F. but below the complete fusing temperature of the dross, that drosses may be produced that contain over 12% tin.

At satisfactory stirring speeds a vortex is.produced which is filled quickly with dross approximating that shown in Fig. 1 of the drawing. With such vortex about the impeller 6 the dross containing lead-oxide can descend to the impeller and be disintegrated and thrown out and scattered through the molten bath so,that the lead oxide will combine with tin to produce tin-oxide. At the same time air associated with the dross in the vortex will also be thrown out into the molten bath, and any unreacted. will escape through the surface of the molten metal and thedross resting thereon. The drosses containing tin-oxide and lead-oxide are present as very finely divided powdered material, and it is accordingly important that intimate contact be established between these fine. particles and the molten bath. By throwing the particles outward from the impeller at high speed they travel through a. large part of the bath, and thus have a chance to react with whatever tin the bath contains.

The process of the invention operates satisfactorily with lead and tin alloys containing small or large amounts of other metals such as for example, antimony, arsenic and silver. It has been found that when treating lead containing tin and large amounts of antimony and arsenic that the elimination of tin is slightly faster than where these elements are not present. This may be due to the fact that antimony-oxide and arsenic-oxide, which are formed by the primary oxidation, act similarly to lead-oxide, and that the reaction of all three oxides simultaneously with the tin causes a more rapid reaction.

The following examples represent preferred embodiments of the invention. It is to be understood that these examples are purely illustrative and the invention is not to be limited thereby except as indicated in the appended claims.

Example 1 The kettle I, which is open to the air. is charged with approximately 75,000 pounds of molten metal assaying: I

After charging the kettle the oil burner is used to bring the temperature of the kettle up to V '1000-1100 F. The mixer or stirrer is placed in a manner such that the impeller is in the exact center of the kettle. 'I'hereupon the stirring apparatus is securely fastened to prevent movement. The mixer is started and maintained at a speed of 1200-1500 R. P. M. giving at least about 3450 ft. per minute peripheral speed, using an 11 inch impeller. At this speed a vortex is formed whose walls are very steep and almost parallel to the shaft 5. If necessary a small amount of heat is supplied to maintain the initial temperature. As the stirring and heating continue, primary oxidation by the air starts, whereby tin-oxide, lead-oxide, antimony-oxide and arsenic-oxide are formed. The silver remains substantially 'unoxidized. The lead and other oxides then react with tin in the bath to form tinoxide by replacement reactions liberating lead as the metal to the bath. These replacement reactions are exothermic and the temperature of the bath rises. The heat from the burner H is cut off or regulated so that the temperature of the bath is maintained at about 1130 F. It is important to observe the temperature closely as it rises rapidly when the reactions occur in the kettle and when heat is being supplied from theoil burner at the same time. The rise is so rapid that in a few minutes the charge may be so hot as to endanger the kettle where it is made of cast iron or steel. If shutting off the oil burner fails to control the heat, it may be further controlled by slowing down the mixer. As the formation of tin-oxide proceeds by direct and replacement oxidation, heat continues to be given oil by the reaction involved. With the charge specified in this example, a light'flre from the oil burner is required for about 10 minutes for every 2 hours in order to hold the temperature within the limits desired. The stirring is continued until the desired concentration of tin in the dross and removal of tin from the metal is secured. The length of time required is dependent upon the temperature, the amount of dross present, the tin content of the dross and As the reaction proceeds the dross layer becomes. thicker and should be removed from time to time.

The rate of oxidation shown for the metal employed in this example is as follows:

Percent Sn Percent Sn g in metal dross l. 05 l. 02 10. 91 0. 86 i9. 84 0. 74 20. as 0. 68 29. 76 0. 56 34. 60

varying between 1060-1160 F. for 4 hours.

At the end of the 5 hour period, 1250 pounds of dross had been skimmed which analyzed as follows:

was placed in the kettle and stirring commenced, the operation being conducted under similar conditions as those given in Example 1. The metal was treated at stirring speeds of about 1200-1500 R. P. M. with an 11 inch impeller at temperatures The tin assay of the metal and percentage of tin in the dross is shown in the following tabulation:

Percent Sn Percent Sn Hours swung in metal in dross The dross removed weighed 1956 pounds andassayed as follows:

Tin per cent 32.36 Antimony 1 do 5.84 Arsenic do .12 Lead do 52.2 Silver per ton ounces 35 and the metal analyzed:

Tin per cent .06 Antimony do 6.39 Arsenic do' .38 Silver per ton ounces 118 Lead Balance Example 3 The following is an example showing the production of a somewhat higher content of tin in the final dross. The starting metal contains a somewhat higher percentage of antimony than given in the two preceding examples. The kettle is charged with approximately 71,000 pounds of molten metal assaying:

Tin per cent 1.46 Antimony do 14.88 Arsenic do 1.08 Silver per ton ounces 5.20 Lead Balance Stirring was commenced and. the operations were conducted under similar conditions as those given in Example 1. The metal 'was treated at stirring speeds of about 1200-1400 R. P. M. with an 11 inch impeller at temperatures varying between 10701140 F. for four hours. The tin assays of the metal and the percentage of tin in the dross is shown in the following tabulation:

Percent Sn Percent Sn Hours snmng in metal in dross Thedross removed weighed 2276 pounds and assayed as follows:

Tin per cent 43.68 Antimony -'do 6.10 Arsenic do .53 Silver per ton ounce .50 Lead per cent 33.80

- The metal analyzed:

Tin per cent .24 Antimony do 15.07 Arsenic do 1.08 Silver per ton ounces 4.80

Example 4 The following is an example showing the production of a trace of tin in the final metal. The kettle is charged with approximately 75,000 pounds of molten metal assaying:

Tin per cent-.. 1.07 Antimony do 6.32 Arsenic do .26 Silver per ton -ounces 118.4

Lead Balance Stirring was commenced and the operations were conducted under similar conditions as those given in Example 1. The metal was treated at stirring speeds of about 1320-1500 R. P. M. with an 11 inch impeller at temperatures varying from 1100-1160 F. The tin assays of the metal and the percentage of tin in the dross is shown in the following tabulation:

. Percent Sn Percent Sn Hours swung in metal in dross Trace 32. 76

The dross removed weighed 2680 pounds and assayed as follows:

Tin per cent 32.76 Antimony do.. 4.02 Arsenic Trace Silver per ton ounces 35.0 Lead per cent 47.6 The metal analyzed:

Tin j Trace Antimony per c 6.46 Arsenic m--- .26 silver per ton ounces 120.0 Lead. Balance In the above examples, only one removal of the dross layer was made and that removal occurred at the end of the operation. Normally, a 2-4 inch dross layer is suflicient to produce the desired tin content in the dross and if the dross layer becomes thicker than 4 inches, it is preferable to remove it.

The metal obtained as a result of the above examples may be employed as desired. The dross may be smelted or otherwise treated to recover the metal constituents.

The tin in the above examples can be reduced to 005% or less by continuing the operation.

The replacement reactions occurring in accordance with the above examples probably include the following;

Other reactions and more complicated combinations of the above may also be taking place.

The color changes in the dross are indications as to the progress of the operation. At first the oxide formed will be yellow, but this changes to gray as the oxidation proceeds. The initial yellow dross contains little tin, while the light gray dross contains well over 30% tin.) If the process is continued, the color changesback through gray to a superficial yellow and the return of the yellow coloration appears-to be a litharge skim on the individual dross particles. This occurs when the tin concentration of the lead is very low and consequently the litharge or lead-oxide formation is more rapid than tin-oxide formation.

During the early stages of operation, the dr appears to be formed at approximately a rate of 600-700 pounds per hour, using metal charges of" tended to refer tolitharge PbO, either aloneor in combination with one or'mo're other oxides such as for example antimony or arsenic-oxide.

We claim:

1. A process for separating tin from impure lead which comprises stirring a mass containing lead oxide and air into a molten bath of such lead at a temperature above about 950 ,F. with a disintegrating impeller inmiersed in 'the bath,

at a speed of at least about 900 R. P. M. to form a vortex extending to the impeller, thereby caus ing a stream containing said lead oxide and some air to pass into the vortex and into contact with the impeller, the latter being .of a character including shape and size to disintegrate the stream containing lead oxide at the speed mentioned, projecting the disintegrated stream by the impeller into the metal bath and mixing it therewith.

2. A process for separating tin from impure lead which comprises stirring a mass containing lead oxide and air into a molten bath of such 3. A process for separating tin from impure lead which comprises stirring a molten bath-of such lead at above 950 F. with a disintegrating immersed impeller at a speed of at least. about 900 R. P. M. to form a vortex extending to the impeller to oxidize the bath and form a dross containing tin oxide and appreciable amounts of lead oxide, thereby causing a stream of said oxides and some air to pass into the vortex and into contact with the impeller, the latter being of a character to disintegrate the stream of oxides at the speed mentioned, projectingthe disintegrated stream by the impeller into the metal bath and mixing it therewith.

4. A process according to claim 3 in which the temperature is maintained within the range of approximately 1000 to 1200 F.

5. A process for separating tin from impure lead which comprises stirring a molten bath of such lead containing tin at a temperature of,

above about 950 F. with an immersed impeller; comprising radial projections operated at a speed of about 900 to 180@' R. P. M. to form a vortex extending to the impeller, causing the dross formed to pass into the vortex with some air into contact with the impeller, the latter being of a suitable size to disintegrate the stream of dross at the speed mentioned, projecting the disintegrated stream by the impeller into the metal bath and mixing therewith.

6. A process for separating tin from impure lead which comprises stirring a molten bath of such lead at above 950 F. with a disintegrating impeller at a speed of at least about 900 R. P. M.

to form a vortex extending to the impeller to oxidize the bath and form a dross containing tin oxide and appreciable amounts of lead oxide, thereby causing a stream of said oxides and some air to pass into the vortex and into contact with the impeller, the latter having aseries of projecting radial arms, each provided with aflat face forming the leading face when the impeller is rotated, projecting the disintegrated stream by the impeller into the metal bath and mixing sit therewith to produce a dross containing at least 25% till.

THOMAS E. HARPER, JR.

GUSTAVE REINBERG. 

